1. Field of the Invention
The present invention relates to a thin plate stack assembly formed by stacking a plurality of metallic thin plates and connecting the thin plates to one another, for example, a thin plate stack assembly which can be used as a core for transformer, etc., and a process of manufacture thereof.
2. Description of the Related Art
Up to now, thin plate stack assemblies wherewith a number of metallic thin plates are stacked, being connected to one other, are known. Such thin plate stack assemblies are used for various applications, such as a core for transformer, etc. With conventional thin plate stack assemblies, upper and lower thin plates are connected to each other by various methods, and one of the connecting methods, which is known, is, as shown in FIG. 12, to form a protrusion 4 in the same location of each metallic thin plate 1 which is circular when viewed from above in the figure, having a convex portion 2 on the upper surface side and a concave portion 3 on the lower surface side, by deforming each metallic thin plate 1 so that it has an upward protrusion, and insert the convex portion 2 of each thin plate 1 into the concave portion 3 of a thin plate 1 disposed just above it so that the convex portion 2 bites into the concave portion 3 to connect vertically stacked thin plates 1 to one other. According to such a connecting method, simply by press working each thin plate 1 to protrude and form the protrusion 4, and thereafter, stacking and pressing them, a thin plate stack assembly having the thin plates 1 connected to one another can be formed, and thus, a large quantity of thin plate stack assemblies can be manufactured simply, inexpensively, and at high speed.
However, the connecting method presents a problem in that thin plates having an extremely small plate thickness, for example, thin plates with a plate thickness of 0.1 mm cannot be satisfactorily connected to one another.
In other words, the protrusion 4 in the method is formed, as shown in FIG. 13, by using a punch 5 having a circular cross section and a die 7 having a hole portion 6 with a circular cross section which corresponds to the cross-sectional geometry of the punch 5, and as illustrated, pressing the punch 5 against the thin plate 1 to protrude a part of the thin plate 1. However, in this case, if the diameter D2 of the hole portion of the die is made too large for the diameter D1 of the punch cross section, the diameter of the convex portion 2 on the upper surface side becomes too large compared to the diameter of the concave portion 3 on the lower surface side, resulting in it being impossible to insert the convex portion 2 into the concave portion 3. The diameter D2 of the hole portion of the die is therefore set at a value slightly larger than the diameter D1 of the punch cross section so that, in stacking, the convex portion 2 is inserted into the concave portion 3 with sufficient force for the convex portion 2 biting into the concave portion 3 to connect the thin plates 1 to one another.
Resulting from the diameter D2 of the hole portion of the die thus being set at a value slightly larger than the diameter D1 of the punch cross section, increasing the amount of protrusion, P, can cause cracks to initiate in the peripheral edge potion 4a of the protrusion 4, and thus, generally, the upward protrusion can be formed to at most approximately half of the plate thickness t. For this reason, as the plate thickness is decreased, the amount of upward protrusion, P, must be decreased. For example, when the plate thickness is 0.1 mm, the amount of protrusion, P, must be at most 0.05 mm, and with such a degree of amount of protrusion, satisfactory biting into the concave portion 3 of a thin plate disposed just above cannot be provided, which makes it difficult to obtain the required connecting force. In other words, with a thin plate having an extremely small plate thickness, such as a thin plate with a plate thickness of 0.1 mm, a problem is presented where it is difficult to connect the thin plates to one another using such a connecting method.
The purpose of the present invention, taking the above-stated situation into consideration, is to provide a thin plate stack assembly which can be favorably and simply produced by connecting thin plates, if they have an extremely small plate thickness, and a process of manufacture thereof.